Hi STx and Peter,
I've had a listen recently to 648, Yes it's different, As you say STx, bass is reduced
and so is the top end harshness. Would possibly be nicer, if the Low bass was brought
up a bit around 100hz, and the Very high end around 5khz or so
Could be done in its Pre-Equaliser, where the bass especially, has lots of adjustments provided

As you say, the bandwidth is much better than other AM stations, who often roll of at 5.5khz
The DSPX AM seems to have a very good digital roll off filter

Although the Mi-Amigo Mod. in the 70's, as Freddie A says, was good (and Radio Veronica's),
My reference for comparison, would have to be, from the Ross in the 80's....

To say it was Amazing, is an Understatement...I would love to know, what the settings were
on the top end Pre-emphasis card, as it was almost an FM type quality
But suppose daytime, if you're a pirate, did it matter? as channels either side of 963 were not used

With processing, Less is more, Apt comment by early composer Claude Debusey was...
"Music is the Space Between the Notes" so with processing, this means the pauses or gaps
need to be there, and not excessively compressed

Rod Watts